My Charlie-girl has the same problem which flares up from time to time. I give her sub-Q fluids twice a week, and basically encourage her to drink and pee as much as possible...I have lots of water bowls which are kept very clean and filled with fresh water once or twice daily. The litterboxes are kept immaculate.

When she flares up and winds up in too much pain to urinate, I usually do put her on a SHORT course of pred to make her feel better ASAP.

She hasn't had a flare-up since I put her on canned food, so I'm keeping my fingers crossed that it keeps her healthy!